Questions that often come up are, "How do magnets work?", or,
"Why is iron magnetic?", or, "What makes a magnet?", or,
"What is the magnetic field made of?".

Those are good questions, and deserve a good answer. However, did you
know that there is a lot about magnets at the atomic level that isn't known
yet? Just like with most of the other basic forces we are familiar with,
such as gravity, electricity, mechanics and heat, scientists start by trying to
understand how they work, what they do, are there any formulas that can be made
to describe (and thus predict) their behavior so we can begin to control them,
and so on.

The work always starts by simple observation (that's the fancy word for
playing around with the stuff!). That's why it's so important to have some
"hands-on" experience with magnets. Have you taken two magnets
and tried to push like poles together? How far away do you start to feel
the repulsion? How does the force vary with the distance between
them? When the magnets are moved off-axis to each other (moving them to
the side and not head on) what does it feel like? Could you describe it
like trying to push two tennis balls together? When you flip one around,
what changes? What about moving one around the other in a circle?
Try these things! That's how you learn! Only when you play with
(observe) them will you begin to understand how they work. This is the stuff
great scientific pioneers did, like Faraday, Lenz, Gilbert, Henry and
Fleming.

What we can find out this way, is some of the basics of magnetism, like:

the north pole of the magnet points to the geomagnetic
north pole (a south magnetic pole) located in Canada above the Arctic
Circle.

north poles repel north poles

south poles repel south poles

north poles attract south poles

south poles attract north poles

the force of attraction or repulsion varies inversely
with the distance squared

the strength of a magnet varies at different locations
on the magnet

magnets are strongest at their poles

magnets strongly attract steel, iron, nickel, cobalt,
gadolinium

magnets slightly attract liquid oxygen and other
materials

magnets slightly repel water, carbon and boron

and so on

Now, the fun begins. We start to ask the question,
"Why?" This is what scientists continually do - try to figure
out why things behave the way they do. Once we figure that out, we have
a better handle on how to apply them to make useful tools for us, right?

Let me share with you some of what is known about how magnets work.
All of the questions have NOT been answered, perhaps you will help answer some
of them. So, some of what is known are simply observations, some are
guesses, but a lot has been figured out.

Atomic Magnetism

There are only a few elements in the periodic table that are attracted to
magnets. None of the elements, by themselves, make good permanent
magnets, but can become temporary magnets (when close to another
magnet). When alloys of various metals are made, some of these alloys
make very good magnets. Why? We don't really know, but we can
observe some consistent rules.

As you know, we have seen that when current flows in a wire, a magnetic
field is created around the wire. Current is simply a bunch of moving
electrons, and moving electrons make a magnetic field. This is how
electromagnets are made to work. This will be important to keep in mind
as we zoom into the structure of atoms.

Around the nucleus of the atom, where the protons and neutrons live, there
are electrons whizzing around. We used to think that they had certain
circular orbits like the planets have around the sun, but have discovered that
it is much more complicated, and much more exciting! Instead, the
patterns of where we would likely find the electron within one of these
orbitals takes into account Schroedinger's wave equations. Pictures of
each of these orbitals can be found at http://www.shef.ac.uk/chemistry/orbitron/index.html.
(These also take into account Heisenberg's uncertainty principle and
probability theory.)

First, electrons can be thought of as occupying certain shells that
surround the nucleus of the atom. These shells have been given letter
names like K,L,M,N,O,P,Q. They have also been given number names, such
as 1,2,3,4,5,6,7. (This is what quantum mechanics is all about).

Within the shell, there may exist subshells or orbitals, with letter names
such as s,p,d,f. Some of these orbitals look like spheres, some
look like an hourglass, others look like beads on a bracelet.

The K shell contains an s orbital. Called a 1s orbital.
The L shell contains an s and p orbital. Called a 2s and 2p orbital.
The M shell contains an s, p and d orbital. Called a 3s, 3p and 3d
orbital.
The N, O, P and Q shells each contain an s, p, d and f orbital. Called a
4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 6f, 7s, 7p, 7d and 7f orbital.

These orbitals also
have various sub-orbitals.

The s orbital can contain only 2 electrons and has no sub-orbitals.
The p orbital can contain 6 electrons, 2 in each of its 3 sub-orbitals,
like px, py and pz.
The d orbital can contain 10 electrons, 2 in each of its 5 sub-orbitals, like
dxy, dxz, dyz, dz2, dx2-y2.
The f orbital can contain 14 electrons, 2 in each of its 7 sub-orbitals.
(And there is a g orbital that can contain 18 electrons, 2 in each of its 9
sub-orbitals, for highly excited electrons.)

A maximum of 2 electrons can occupy a sub-orbital where one has a spin of
UP, the other has a spin of DOWN. There can not be two electrons with
spin UP in the same sub-orbital. (Pauli exclusion principal.)
Also, when you have a pair of electrons in a sub-orbital, their combined
magnetic fields will cancel each other out.

In order to show how many electrons are in each orbital, the following
convention is sometimes used:Chlorine
has 1s22s22p63s23p5
for a total of 17 electrons. This tells us that there are 2 in 1s, 2 in
2s, 6 in 2p, 2 in 3s, and 5 in 3p.

Let's look at the pattern of how the electron
orbitals are filled as we move up in the periodic
table of the elements. (This is a fantastic site on the
elements!!!)

As you can see, the general order for filling the electron orbitals follows
a sequence since the energy level for each orbital increases in this sequence:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

After each orbital is full, it starts to fill the next one in this
sequence. There are a few odd jumps in the sequence when you get to
filling the 4f, 5d and 6p orbitals, but that's how it goes.

If we were to examine Iron
(atomic number 26), Cobalt
(27), Nickel
(28) and Gadolinium
(64), all of which are considered ferromagnetic since they are strongly
attracted to a magnet, it is difficult to see what makes them so different
from the other elements next to them or below them in the periodic
table. In other words, if Iron is so strongly magnetic, why isn't
Manganese? Perhaps there are other factors
we need to take into account such as the crystalline structure. But it
is generally accepted that these ferromagnetic elements have large magnetic
moments due to un-paired electrons in their outer orbitals. This is like
having current flowing in a coil of wire, creating a magnetic field.
Even the spin of the electron is thought to create a minute magnetic
field. When you get a bunch of these fields together, they add up to
bigger fields.

Iron (Fe)
Atomic Number 26
Electron configuration 1s22s22p63s23p63d64s2
This shows the electron orbits as circular rings around the nucleus. It
really isn't like this, but it makes a good diagram.
The green dot in the center is the nucleus with the 26 protons and 26
neutrons.
The orange dots in the 3d orbital are the 4 unpaired electrons.
The unpaired electrons in 3d create a magnetic moment, or force. It is
thought that D/r must be 3 or more to create ferromagnetism. This
condition occurs in Iron, Cobalt, Nickel and rare-earth groups.

We can go one level deeper into quantum mechanics. This is where we
ask, "What is the magnetic field made of?"

Today, there are four basic forces that are known: gravity,
electromagnetism, weak, strong. What creates these forces? There
is speculation among particle physicists that these forces are the result of
photons that are exchanged between particles. This exchange is what
creates a repulsion or attraction between various particles, giving us the
forces we call gravity, magnetism, and others that hold the protons together
in the center of the atom. More information on these Virtual
Particles is available at this link.

Magnetic Domains

1. Magnetic moments in neighboring atoms are held parallel by
quantum mechanical forces.

2. These atoms with these magnetic characteristics are grouped
into regions called domains. Each domain has its own North pole and
South pole.

A Domain is the smallest known permanent magnet. About 6000 domains
would occupy an area the size of the head of a common pin.
A domain is composed of approximately one quadrillion (1,000,000,000,000,000
or 1015) atoms.

3. In unmagnetized ferromagnetic materials, the domains are
randomly oriented and neutralize each other or cancel each other out.
However, the magnetic fields are still present within the domains!

(These diagrams show domains as small cubes or squares - kind of a micro
view.)

Here is a sample of unmagnetized iron, showing its domains in random magnetic
orientations (x is arrow away from you = South Pole, dot is arrow toward you =
North Pole)

This shows the magnetic field around that sample of unmagnetized iron with its
groups of domains, like those noted above, with random orientations. As
you can see, this sample has multiple North and South poles where the magnetic
field lines exit and enter the material.

4. The application of an external magnetic field causes the
magnetism in the domains to become aligned so that their magnetic moments are
added to each other and lined up with the applied field.

This shows the magnetic field around a group of domains, where all but one is
oriented in the same direction.

And this shows the magnetic field around a group of domains that are all lined
up together.

With soft magnetic materials such as iron, small external fields will cause
a great amount of alignment. However, because of the small restraining
force only a little of the alignment will be retained when the external field
is removed.

With hard magnetic materials such as Alnico a greater external field must
be applied to cause alignment of the domains, but most of the alignment will
be retained when the field is removed, thus creating a stronger permanent
magnet, which will have one North and one South pole.

If we were to look at this from more of a macro level, a level at which we
have actually seen under microscopes, we would see larger domains - not as
cubes or squares, but more like irregular polygons.

If you were to examine a piece of iron that is not magnetized, you will
find that the domains within the iron will not be pointing in the same
direction, but will be pointing in a bunch of random directions. This
randomness is what causes the magnetic field of each domain to be cancelled
out by the magnetic field of another domain. The result is that there is
no single north pole or south pole. Instead, there are a bunch of north
and south poles all over the place that cancel each other out.

Now, if this piece of iron were placed within an external magnetic
field (created by current flowing in a solenoid), the domains will start to
line up with the external magnetic field. It takes some energy to cause
a domain to re-orient itself. As the external magnetic field becomes
stronger, more and more of the domains will line up with it. (Another
way to look at it is that the domains that are aligned with the external
magnetic field will grow in size, and the others will shrink.) There will be a
condition where all of the domains within the iron are aligned with the
external magnetic field. This condition is called saturation, because
there are no more domains that can be lined up, no matter how much stronger
the magnetic field is made.

(These diagrams show domains as irregular polygons - more of a macro view.)
no external mag
field small
mag
field
larger mag
field
large mag field, saturation of domains

Resulting magnetic field with the domains as indicated above with no external
mag field.
Note that the domains still have their own magnetic field, but that the field
lines stay almost exclusively within the material.
Very little leaks out of the material. This would be an example of
unmagnetized iron.

Resulting magnetic field with the domains as indicated above with small mag
field.
This has two north poles (lower right and upper right) and one very spread-out
south pole (on the left).

Resulting magnetic field with the domains as indicated above with larger mag
field.
Starting to look more like a magnet with a defined north and south pole.

Resulting magnetic field with the domains as indicated above with large mag
field, saturation of domains.
This is what a permanent or temporary magnet would typically look like.

What happens when the external magnetic field is reduced back to
zero? In a soft magnetic material (such as iron or silicon steel), most
of the domains will return to their random orientations, so that you will be
left with a very weak magnet since only a few of the domains will be lined up
in the same direction. In other words, you are back where you started
from. In a hard magnetic material (alloys of iron such as Alnico, some
steels, neodymium-iron-boron, etc), most of the domains will remain aligned,
so that you will be left with a strong magnet. Since the ending point is
not the same as the starting point for magnetic materials, they have what is
called hysteresis.

Magnetic Poles

1. A freely suspended bar magnet will always tend to align itself
with the North and South magnetic poles of the earth. An example of this
is the magnetic compass.

This shows the magnetic lines of force for a long, narrow bar magnet.
North is on the right end.

This shows the magnetic lines of force for a flat, wide magnet. North is
on top.

Note the concentration of lines where they exit or enter the magnet, at the
ends. This is what defines a pole. Since magnetic fields are like
rubber-bands, and since they like to crowd into ferromagnetic material
whenever they can, they bunch up inside the magnet material. Again, since
the field lines are like closed loops, there is always some place where they
enter the magnet (South pole), and some place where they exit the magnet
(North pole). These places are the poles. The magnetic field lines
tend to be closest together there. This is why, if you break a magnet in
half, you will still have a North pole and a South pole, since the lines enter
one magnet, then exit it, then enter the next magnet, then exit it, before it
goes back to the first magnet again. This is also why we can't have a
"monopole" or single pole. If the magnetic field line exits
the magnet, somewhere it will have to enter it again - the loops are closed
like rubber-bands. The minimum number of poles a magnet can have is two
- one each of North and South. However, it is possible for a magnet to
have more than two poles, right? Look at the pictures above again, where
we have a lot of random square domains. See all the poles all around the
periphery of the group of domains? I count about 10! Below is a
magnet with 8 poles.

This magnet has 8 poles - 4 North and 4 South, or 4 pole-pairs.

A compass in the vicinity of a magnet will always point along a tangent to one
of the magnetic field lines.

This occurs because unlike poles of a magnet are always attracted to each
other by the invisible lines of force whereas like poles repel each
other. The earth acts like a large permanent magnet. In fact, the
earth is the largest magnet in the world. But don't forget the sun that
also has a magnetic core, and so do collapsed stars, and they are bigger than
the earth! I wouldn't call the earth a permanent magnet like other
magnets we are used to. Its magnetism is the result of electron
convection currents in the liquid core, and they have flipped around a few
times in the past, just like what the sun does every 11 years. So, it's
really more like an electromagnet.

2. Permanent magnets can be designed and engineered in hundreds of
shapes and sizes to perform various tasks.

For example, the horse-shoe shape is very commonly used in magnetic
separators because its lines of force are mostly at the open end of the
horse-shoe, and this helps in the separation of ferrous materials. A
piece of iron placed within the effective range of the magnetic field will, in
turn become magnetized. It will have its own North and South poles and
will be attracted to the permanent magnet.

Summary

What all this is saying, is that the atoms of ferromagnetic materials tend
to have their own magnetic field created by the electrons that orbit it.

Small groups of about 1015 atoms tend to orient themselves in
the same direction. These groups are called domains. Each domain
has its own north pole and south pole.

If you were to examine a piece of iron that is not magnetized, you will
find that the domains within the iron will not be pointing in the same
direction, but will be pointing in a bunch of random directions. This
randomness is what causes the magnetic field of each domain to be cancelled
out by the magnetic field of another domain. The result is that there is
no single north pole or south pole. Instead, there are a bunch of north
and south poles all over the place that cancel each other out.

Now, if this piece of iron were placed within an external magnetic
field (created by current flowing in a solenoid), the domains will start to
line up with the external magnetic field. It takes some energy to cause
a domain to re-orient itself. As the external magnetic field becomes
stronger, more and more of the domains will line up with it. (Another
way to look at it is that the domains that are aligned with the external
magnetic field will grow in size, and the others will shrink.) There will be a
condition where all of the domains within the iron are aligned with the
external magnetic field. This condition is called saturation, because
there are no more domains that can be lined up, no matter how much stronger
the magnetic field is made.

When the external magnetic field is then removed, soft magnetic materials
will become randomly oriented domains again. However, hard magnetic
materials will keep most of their domains aligned, making it a strong
permanent magnet.

Magnetic field lines are closed loops. They enter a magnet at its
South pole, and exit a magnet at its North pole. The poles may cover a
large area, where the concentration of lines is not uniform.

Scientific Disciplines

Did you notice all of the scientific disciplines that are involved with
magnets? I'll list the ones I can think of, perhaps you can add some to
this list.

NOTE:
Some of the material shared above was originally presented by Arlo F.
Israelson, Chief Engineer at Eriez Manufacturing Co., in Erie, Pennsylvania,
USA, dated 9/12/52. This was found in Permanent Magnet Design and
Application Handbook, by Lester Moskowitz, Cahners Books International,
Boston, MASS 1976, in Chapter 6, Fundamentals of Magnetism. The
illustrations and additional notes are mine, patterned after his presentation.